U.S. patent application number 10/284671 was filed with the patent office on 2003-05-22 for gantry system and x-ray ct system.
This patent application is currently assigned to GE Yokogawa Medical Systems, Limited. Invention is credited to Azu, Katsumi, Maida, Masashi, Moritake, Masahiro, Urabe, Daigo.
Application Number | 20030095635 10/284671 |
Document ID | / |
Family ID | 19165429 |
Filed Date | 2003-05-22 |
United States Patent
Application |
20030095635 |
Kind Code |
A1 |
Moritake, Masahiro ; et
al. |
May 22, 2003 |
Gantry system and X-ray CT system
Abstract
For the purpose of reducing a deviation in the rotational center
of scan and a deviation in scan position in the direction of length
of a rail, a gantry system including a pair of runway rails and a
gantry in an X-ray CT system that can move along the runway rails,
is characterized by comprising a linear guide rail arranged in the
direction along the runway rails and linear guide blocks mounted on
the gantry and slidably fitted on the linear guide rail.
Inventors: |
Moritake, Masahiro; (Tokyo,
JP) ; Maida, Masashi; (Tokyo, JP) ; Azu,
Katsumi; (Tokyo, JP) ; Urabe, Daigo; (Tokyo,
JP) |
Correspondence
Address: |
Patrick W. Rasche
Armstrong Teasdale LLP
Suite 2600
One Metropolitan Sq.
St. Louis
MO
63102
US
|
Assignee: |
GE Yokogawa Medical Systems,
Limited
|
Family ID: |
19165429 |
Appl. No.: |
10/284671 |
Filed: |
October 31, 2002 |
Current U.S.
Class: |
378/198 |
Current CPC
Class: |
A61B 6/548 20130101;
A61B 6/035 20130101 |
Class at
Publication: |
378/198 |
International
Class: |
H05G 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2001 |
JP |
2001-353408 |
Claims
1. A gantry system comprising a pair of runway rails and a gantry
in an X-ray CT system that can move along the runway rails, further
comprising a linear guide rail arranged in the direction along the
runway rails and a linear guide block mounted on the gantry and
slidably fitted on the linear guide rail.
2. The gantry system of claim 1, wherein the linear guide rail is
arranged nearly at the central position of the pair of runway
rails.
3. The gantry system of claim 1, further comprising a linear
encoder for measuring a position in the direction of movement of
the gantry, wherein the linear scale of the linear encoder is
arranged along the direction of movement of the gantry, and wherein
the pickup sensor of the linear encoder is mounted on the gantry in
such a way as to oppose the linear scale.
4. The gantry system of claim 1, wherein the linear scale is
arranged nearly at the central position of the pair of runway
rails.
5. The gantry system of claim 1, further comprising: a storage unit
for storing a distance from a position of a predetermined check
point to an initial scan base position in the direction of movement
of the gantry; a detection unit for detecting that the gantry moves
to the check point; and a setting unit for setting a scan base
position based on a position measured by the linear encoder when
the gantry is moved to the check point and the distance stored in
the storage unit.
6. The gantry system of claim 1, wherein the predetermined check
point includes a first check point and a second check point
positioned between the first check point and the initial scan base
position, wherein the storage unit previously stores a first
distance to show a distance from the first check point to the
second check point and a distance from the second check point to
the initial scan base position, wherein the detection unit includes
a first sensor for detecting that the gantry is moved to the first
check point and a second sensor for detecting that the gantry is
moved to the second check point, and wherein the setting unit sets
a scan base position based on a position measured by the linear
encoder when the gantry is moved to the second check point and the
second distance stored in the storage unit.
7. The gantry system of claim 1, further comprising a judgment unit
for judging whether or not an error between a distance between a
position measured when the gantry is moved to the first check point
and a position measured when the gantry is moved to the second
check point and the second distance stored in the storage unit is
within a predetermined range, and an informing unit for informing a
judgment result of the judgment unit in accordance with the
judgment result.
8. An X-ray CT system for performing a scan of an object to be
inspected while moving a gantry, comprising: a storage unit for
previously storing a distance from a predetermined check point to
an initial scan base position in the direction of movement of the
gantry; a measurement unit for measuring a position in the
direction of movement of the gantry; a detection unit for detecting
that the gantry is moved to the check point; and a setting unit for
setting a scan base position based on a position measured by the
measurement unit when the gantry is moved to the check point and
the distance stored in the storage unit.
9. The X-ray CT system of claim 8, wherein the predetermined check
point includes a first check point and a second check point
positioned between the first check point and the initial scan base
position, wherein the storage unit previously stores a first
distance to show a distance from the first check point to the
second check point and a second distance to show a distance from
the second check point to the initial scan base position, wherein
the detection unit includes a first sensor for detecting that the
gantry is moved to the first check point and a second sensor for
detecting that the gantry is moved to the second check point, and
wherein the setting unit sets a scan base position based on a
position measured by the linear encoder when the gantry is moved to
the second check point and the second distance stored in the
storage unit.
10. The X-ray CT system of claim 9, further comprising a judgment
unit for judging whether or not an error between a distance between
a position measured when the gantry is moved to the first check
point and a position measured when the gantry is moved to the
second check point and the second distance stored in the storage
unit is within a predetermined range, and an informing unit for
informing a judgment result of the judgment unit in accordance with
the judgment result.
11. An X-ray CT system that includes a gantry mounted on a runway
rail and movable along the runway rail and an operating console
connected to the gantry and outputting information relating to scan
to the gantry and performs a scan of an body to be inspected while
moving the gantry, the X-ray CT system comprising: a first
direction unit that is mounted on the gantry and directs the gantry
to move; a second direction unit that is mounted on the operating
console and directs the gantry to move; a storage unit that stores
information of a maximum range in which the gantry is moved by the
first direction unit; and a control unit that controls the movable
range of the gantry by the second direction unit in accordance with
the maximum range in which the gantry is moved by the first
direction unit.
12. The X-ray CT system of claim 11, further comprising a unit for
clearing the information stored in the storage unit in accordance
with a predetermined operation in the gantry or a predetermined
operation in the operating console.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a position control
technology of a gantry in an X-ray CT (Computed Tomography) that
performs a scan to take a tomogram of an object to be inspected
while moving the gantry.
[0002] An X-ray CT system has been known whose gantry is mounted on
a bogie moving on rails by means of wheels and which performs a
scan of an object to be inspected while moving the gantry.
[0003] Generally, in a rail, its cross section is formed convexly
and the convex portion becomes a rail tread surface. A groove
corresponding to the width of the rail tread surface is formed on a
wheel tread surface along the direction of rolling of the wheel
(that is, the wheel tread surface is formed concavely). This groove
is engaged with the rail convex portion to enable the wheel to move
along the rail to thereby prevent the wheel from coming off the
rail.
[0004] In order to roll the wheels on the rails smoothly, a gap of
about 0.5 mm to 1 mm is usually provided between the rail tread
surface and the groove of the wheel tread surface. Four wheels of
the bogie are machined so that they have the same diameter, but
there is a little difference in size between them and the
difference in size causes the bogie to move not in a straight line
but in a little curved line to the left and right side. As the
bogie moves forward, the bogie is deviated-in the lateral direction
to narrow the provided gap gradually and when one side of the
groove comes into contact with one side of the rail, the bogie can
not move further in the deviated direction but is moved straight in
the direction of length of the rail forcibly by the groove and the
rail.
[0005] Next, when the bogie moves in the reverse direction, the
bogie is deviated reversely in the lateral direction and when the
opposite side of the groove comes into contact with the rail, the
bogie is forcibly moved straight in the direction of length of the
rail. That is, the position of the bogie when the bogie moves
forward is deviated in the lateral direction from the position of
the bogie when the bogie moves backward. As a result, there is
presented a problem that the rotational center of scan rotation is
deviated.
[0006] Moreover, while an rotary encoder is mounted on the shaft of
a driven wheel in the related art to detect the position of the
bogie by detecting the rotation of the wheel, as described above,
because the position of the bogie when the bogie moves forward is
deviated in the lateral direction from the position of the bogie
when the bogie moves backward, the wheel does not move in the same
locus when the bogie moves forward and when the bogie moves
backward. For this reason, there is presented a problem that when
the bogie stops at a certain position in the direction of length of
the rail, the detection result of position of the bogie is
different depending on the direction of movement of the bogie
before the stop of the bogie. A problem that a large error is
caused in detecting the position of the bogie results in a
deviation in a scan position in the direction of length of the
rail.
[0007] Moreover, the rotation of the rotary encoder depends on the
size of the wheel. For this reason, there is also presented a
problem that since the detection accuracy of movement distance of
the bogie in the direction of length of the rail depends on the
machining accuracy of the size of the wheel, a desired position
detection accuracy can not be kept.
[0008] Further, there is also presented the following problem:
while the position of the bogie when the bogie moves back and forth
can be recognized by the detection of a limit switch at a retracted
position of the gantry, it is necessary for an operator to press a
button provided on the gantry to set a zero slice position that is
the base of scan (scan base position), which makes operability
worse. In particular, this includes a problem that even if changing
the scan base position is not required because the predetermined
scan base position exists, it is necessary for the operator to
input the scan base position manually, which makes operability
worse and tends to make an operating miss or to cause a position
error.
[0009] Still further, safety must be sufficiently secured when the
gantry is moved.
SUMMARY OF THE INVENTION
[0010] Therefore, it is the object of the present invention to
reduce a deviation in the rotational center of scan and a deviation
in a scan position in the direction of length of a rail in an X-ray
CT system that performs a san of an object to be inspected while
moving a gantry along the rail.
[0011] It is another object of the present invention to increase
accuracy in detecting the position of a gantry in an X-ray CT
system that performs a san of an object to be inspected while
moving the gantry along a rail.
[0012] It is still another object of the present invention to
improve operability in setting a scan base position in an X-ray CT
system that performs a san of an object to be inspected while
moving a gantry along the rail.
[0013] It is still another object of the present invention to
guarantee safety when a gantry is moved in an X-ray CT system that
performs a san of an object to be inspected while moving a gantry
along the rail.
[0014] According to the present invention, there is provided a
gantry system comprising a pair of runway rails and a gantry in an
X-ray CT system that can move along the runway rails, characterized
by a linear guide rail arranged in the direction along the runway
rails and a linear guide block mounted on the gantry and slidably
fitted on the linear guide rail.
[0015] Further, according to the present invention, there is also
provided an X-ray CT system for performing a scan of an object to
be inspected while moving a gantry, comprising: a storage unit for
previously storing a distance from a predetermined check point to
an initial scan base position in the direction of movement of the
gantry; a measurement unit for measuring a position in the
direction of movement of the gantry; a detection unit for detecting
that the gantry is moved to the check point; and a setting unit for
setting a scan base position based on a position measured by the
measurement unit when the gantry is moved to the check point and
the distance stored in the storage unit.
[0016] Still further, according to the present invention, there is
provided a method of controlling an X-ray CT system that includes a
gantry mounted on a runway rail and movable along the runway rail,
a measurement unit for measuring a position in the direction of
movement of the gantry, a detection unit for detecting that the
gantry is moved to a predetermined check point, and a storage unit
for previously storing a distance from the predetermined check
point to an initial scan base position in the direction of movement
of the gantry, and that performs a scan of a body to be inspected
while moving the gantry, the method comprising: a detection step of
detecting that the gantry is moved to the predetermined check point
by the detection unit; a measurement step of measuring a position
when the gantry is moved to the predetermined check point by the
measurement unit; and a setting step of setting a scan base
position based on a position measured at the measurement step and
the distance stored in the storage unit.
[0017] Still further, according to the present invention, there is
provided a program for controlling an X-ray CT system that includes
a gantry mounted on a runway rail and movable along the runway
rail, a measurement unit for measuring a position in the direction
of movement of the gantry, a detection unit for detecting that the
gantry is moved to a predetermined check point, and a storage unit
for previously storing a distance from the predetermined check
point to an initial scan base position in the direction of movement
of the gantry, and that performs a scan of a body to be inspected
while moving the gantry, the program comprising the program codes
of: a detection step of detecting that the gantry is moved to the
predetermined check point by the detection unit; a measurement step
of measuring a position when the gantry is moved to the
predetermined check point by the measurement unit; and a setting
step of setting a scan base position based on a position measured
at the measurement step and the distance stored in the storage
unit.
[0018] Still further, according to the present invention, there is
also provided a storage medium storing a program for controlling an
X-ray CT system that includes a gantry mounted on a runway rail and
movable along the runway rail, a measurement unit for measuring a
position in the direction of movement of the gantry, a detection
unit for detecting that the gantry is moved to a predetermined
check point, and a storage unit for previously storing a distance
from the predetermined check point to an initial scan base position
in the direction of movement of the gantry, and that performs a
scan of a body to be inspected while moving the gantry, the storage
medium storing the program codes of: a detection step of detecting
that the gantry is moved to the predetermined check point by the
detection unit; a measurement step of measuring a position when the
gantry is moved to the predetermined check point by the measurement
unit; and a setting step of setting a scan base position based on a
position measured at the measuring step and the distance stored in
the storage unit.
[0019] Still further, according to the present invention, there is
provided a method of controlling an X-ray CT system that includes a
gantry mounted on a runway rail and movable along the runway rail,
a measurement unit for measuring a position in the direction of
movement of the gantry, a detection unit for detecting that the
gantry is moved to predetermined first and second check points, and
a storage unit for previously storing a first distance to show a
distance from the first check point to the second check point and a
second distance to show a distance from the second check point to
an initial scan base position, in the direction of movement of the
gantry, and that performs a scan of an object to be inspected while
moving the gantry, the method comprising: a first detection step of
detecting that the gantry is moved to the first check point by the
detection unit; a first measurement step of measuring a position
when the gantry is moved to the first check point by the
measurement unit; a second detection step of detecting that the
gantry is moved to the second check point by the detection unit; a
second measurement step of measuring a position when the gantry is
moved to the second check point by the measurement unit; and a
setting step of setting a scan base position based on a position
measured at the second measurement step and the second distance
stored in the storage unit.
[0020] Still further, according to the present invention, there is
provided a program for controlling an X-ray CT system that includes
a gantry mounted on a runway rail and movable along the runway
rail, a measurement unit for measuring a position in the direction
of movement of the gantry, a detection unit for detecting that the
gantry is moved to predetermined first and second check points, and
a storage unit for previously storing a first distance to show a
distance from the first check point to the second check point and a
second distance to show a distance from the second check point to
an initial scan base position, in the direction of movement of the
gantry, and that performs a scan of an object to be inspected while
moving the gantry, the program comprising the program codes of: a
first detection step of detecting that the gantry is moved to the
first check point by the detection unit; a first measurement step
of measuring a position when the gantry is moved to the first check
point by the measurement unit; a second detection step of detecting
that the gantry is moved to the second check point by the detection
unit; a second measurement step of measuring a position when the
gantry is moved to the second check point by the measurement unit;
and a setting step of setting a scan base position based on a
position measured at the second measurement step and the second
distance stored in the storage unit.
[0021] Still further, according to the present invention, there is
also provided a storage medium storing a program for controlling an
X-ray CT system that includes a gantry mounted on a runway rail and
movable along the runway rail, a measurement unit for measuring a
position in the direction of movement of the gantry, a detection
unit for detecting that the gantry is moved to predetermined first
and second check points, and a storage unit for previously storing
a first distance to show a distance from the first check point to
the second check point and a second distance to show a distance
from the second check point to an initial scan base position, in
the direction of movement of the gantry, and that performs a scan
of an object to be inspected while moving the gantry, the storage
medium storing the program codes of: a first detection step of
detecting that the gantry is moved to the first check point by the
detection unit; a first measurement step of measuring a position
when the gantry is moved to the first check point by the
measurement unit; a second detection step of detecting that the
gantry is moved to the second check point by the detection unit; a
second measurement step of measuring a position when the gantry is
moved to the second check point by the measurement unit; and a
setting step of setting a scan base position based on a position
measured at the second measurement step and the second distance
stored in the storage unit.
[0022] Still further, according to the present invention, there is
also provided an X-ray CT system that includes a gantry mounted on
a runway rail and movable along the runway rail and an operating
console connected to the gantry and outputting information relating
to scan to the gantry and performs a scan of an body to be
inspected while moving the gantry, comprising: a first direction
unit that is mounted on the gantry and directs the gantry to move;
a second direction unit that is mounted on the operating console
and directs the gantry to move; a storage unit that stores
information of a maximum range in which the gantry is moved by the
first direction unit; and a control unit that controls the movable
range of the gantry by the second direction unit in accordance with
the maximum range in which the gantry is moved by the first
direction unit.
[0023] According to the present invention, in an X-ray CT system
that performs a scan of a body to be inspected while moving a
gantry along rails, it is possible to reduce a deviation in the
rotational center of scan and a deviation in scan position in the
direction of length of the rail.
[0024] Further, according to the present invention, in an X-ray CT
system that performs a scan of a body to be inspected while moving
a gantry along rails, it is possible to increase the accuracy of
detecting the position of the gantry.
[0025] Still further, according to the present invention, in an
X-ray CT system that performs a scan of a body to be inspected
while moving a gantry along rails, it is possible to improve
operability in setting the scan base position.
[0026] Still further, according to the present invention, in an
X-ray CT system that performs a scan of a body to be inspected
while moving a gantry along rails, it is possible to ensure safety
when the gantry is moved.
[0027] Further objects and advantages of the present invention will
be apparent from the following description of the preferred
embodiments of the invention as illustrated in the accompanying
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0028] FIG. 1 is an external perspective view to show one example
of a gantry mounted on rails in an embodiment.
[0029] FIG. 2 is a side view of the gantry in the embodiment.
[0030] FIG. 3 is an illustration to show the relationship between
wheel and side rail in the embodiment.
[0031] FIG. 4 is a top perspective view of side rails, a center
rail, and the gantry.
[0032] FIG. 5 is an illustration to show one example of a state
where a linear guide block is mounted on a linear guide rail.
[0033] FIG. 6 is a cross-sectional view taken on a line A-A in FIG.
5.
[0034] FIG. 7 is a block diagram to show the constitution of a
control board built in a gantry base part in the embodiment.
[0035] FIG. 8 is an illustration to show one example of an
operating panel in the embodiment.
[0036] FIG. 9 is a flow chart to show a process of initially
setting the positional relations of a first limit switch, a second
limit switch, and a desired scan base position, respectively.
[0037] FIG. 10 is a flow chart to show a processing of setting a
scan base position in the embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Modes for carrying out the invention will be described in
detail with reference to the drawings.
[0039] FIG. 1 is a schematic perspective view to show one example
of a gantry in an X-ray CT system mounted on rails in a mode for
carrying out the invention.
[0040] As shown in FIG. 1, a gantry 1 has a gantry base part 2 and
is mounted on a pair of side rails 3a and 3b. The gantry 1 can move
along the side rails 3a, 3b and while the gantry 1 moves, a scan is
performed. Moreover, a center rail 4 is disposed at the central
position sandwiched between the side rails 3a and 3b in the
direction along the side rails 3a and 3b. The structure of the
center rail 4 will be described later.
[0041] For the sake of convenience in the following description,
let's define a direction of disposition of the side rails 3a and
3b, that is, a direction in which the gantry moves, as a z-axis
direction, a direction along a floor and perpendicular to the
z-axis direction as an x-axis direction, and a direction
perpendicular to the floor (vertical direction) as a y-axis
direction.
[0042] FIG. 2 is a side view of the gantry 1 shown in FIG. 1. As
shown in FIG. 1, wheels rolling on the side rails are provided in
the gantry base part 2 (wheels 5, 6 rolling on the side rail 3a are
shown in FIG. 2). This enables the gantry 1 to move in the z-axis
direction.
[0043] FIG. 3 is an illustration to show the relationship between
the wheel 5 and the side rail 3a. As shown in FIG. 3, the side rail
3a is formed convexly in its cross section and its protruding
portion becomes a rail tread surface. Moreover, a groove
corresponding to the width of the rail tread surface is formed on
the wheel tread surface of the wheel 5 along the direction in which
the wheel rolls. That is, the wheel tread surface is formed
concavely. Then, the groove is engaged with the rail's protruding
portion to enable the wheel 5 to move along the rail 3a to thereby
prevent the wheel from coming off the rail. This holds true also
for the other wheels.
[0044] FIG. 4 is a top perspective view to show the side rails 3a
and 3b, the center rail 4, and the gantry 1 which are shown in FIG.
1.
[0045] As described above, the wheels 5, 6 are set on the side rail
3a whereas wheels 7, 8 are set on the other side rail 3b. The
wheels 6 and 8 are connected to each other by a shaft 9 and are
driven by a motor 11 via a gear 10 (both of them are mounted in the
gantry base part 2). That is, the wheels 6, 8 are driving wheels
and the wheels 5, 7 are driven wheels.
[0046] A linear guide rail 41 is mounted on the center rail 4 in
the z-axis direction. Then, two linear guide blocks 42, 43 mounted
on the bottom surface of the gantry base part 2 are mounted on the
linear guide rail 41 so that they can slide on the linear guide
rail 41. FIG. 5 shows one example of a state in which the linear
block 42 is mounted on the linear guide rail 41 and FIG. 6 shows a
cross-sectional view taken on a line A-A in FIG. 5. Referring to
this cross-sectional view makes it clear that the linear guide
block 42 is fitted on the linear guide rail 41 with bearings 45a,
45b interposed between their side surfaces. Such structure enables
the linear guide block 42 to slide along the linear guide rail 41.
This holds true also for the linear guide block 43.
[0047] Moreover, in order to absorb errors in height of the side
rails 3a, 3b and the center rail 4, respectively, the linear guide
block 42 is mounted on the bottom surface of the gantry base part 2
with a gap of about several millimeters in the y-axis direction so
that it can slide thereon.
[0048] Measuring the position of the gantry 1 in the z-axis
direction (also simply referred to as a position detection) in the
embodiment is performed by the use of a linear encoder. First, a
linear scale 50 of the linear encoder is mounted on the center rail
4 along the linear guide rail 41. Further, a pickup sensor 51 is
mounted on the gantry base part 2 so as to oppose the linear scale
50. The outputs of this pickup sensor 51 (A-phase and B-phase
encoder signals) are sent to a control board 100 (see FIG. 4) and
the position of the gantry 1 in the z-axis direction can be
measured based on this outputs.
[0049] Since the two linear guide blocks 42, 43 mounted on the
bottom surface of the gantry base part 2 are fitted in this manner
on the linear guide rail 41 mounted on the center rail 4 so that
they can freely slide, the deviation of the gantry 1 in the x-axis
direction with respect to the movement of the gantry 1 in the
z-axis direction is forcibly limited. Therefore, even if the gaps
between the grooves of the wheels 5, 6, 7, 8 and the rails 3a, 3b
apply forces to the gantry 1 in the x-axis direction as the gantry
1 moves or apply a force for changing the direction of the gantry 1
gradually to the gantry 1 as the gantry 1 moves, the gantry 1 is
not deviated by the forces but can be moved correctly straight.
[0050] This can reduce a deviation in the rotational center of scan
and a deviation in a scan position in the z-axis direction.
[0051] Further, it is possible to detect the position of the gantry
1 in the z-axis direction with high accuracy without being affected
by the machining accuracy such as the size of the wheel and the
direction of an axle. Moreover, since the linear scale 50 is
mounted on a lower portion near the center in the x-direction of
the gantry 1, even if a force of torsion is applied to the gantry
base part 2 to deform the gantry base part 2, it is possible to
detect the scan position correctly.
[0052] Next, an operation of moving the gantry 1 will be described.
Here, referring to FIG. 4, on the right side of paper is provided a
table (not shown) on which a body to be inspected is placed. In the
following description, in the direction of movement of the gantry
1, that is, in the z-axis direction, let's call a direction in
which the gantry is brought near to the table as an IN side and a
direction in which the gantry is brought away from the table as an
OUT side.
[0053] Further, in FIG. 4, on the bottom surface of the gantry base
part 2 are mounted a first limit switch S1 and a second limit
switch S2. Moreover, a protrusion 52 for operating the first limit
switch S1 is provided on an outside movement limit position (OUT
limit position) as a first check point on the center rail 4 and a
protrusion 53 for operating the second limit switch S2 is provided
on a predetermined position sandwiched between the protrusion 52
and the table as a second check point on the center rail 4. These
protrusions 52, 53 are used in a processing of setting the scan
base position that will be described later.
[0054] FIG. 7 is a block diagram to show the constitution of the
control board 100 (see FIG. 4) built in the gantry base part 2.
[0055] In FIG. 7, a reference numeral 61 denotes a CPU for
controlling the movement of the gantry 1 and a reference numeral 62
denotes a ROM for storing the operation processing procedure
(program) of the CPU 61 and a reference character 63a denotes a RAM
functioning as a main storage and a reference character 63b denotes
a flash memory functioning as an auxiliary storage. A reference
numeral 64 denotes an interface for inputting data from an operator
console 200 for outputting information relating to scan to the
gantry 1. Reference numerals from 65 to 68 denote an operating
panel 20, the first limit switch S1, the second limit switch S2,
and an interface for inputting data from the pickup sensor 51. A
reference numeral 69 denotes an up/down counter indicting a
relative position in the z-axis direction based on the A-phase and
B-phase encoder signals from the pickup sensor 51 and a reference
numeral 70 denotes a motor driver for performing the driving
control of the motor 11.
[0056] Before performing a scan, for example, after turning on the
power, an operation of moving the gantry 1 once on the IN side and
the OUT side by a manual operation to make a check that moving the
gantry 1 does not cause a danger is performed. The movement of the
gantry 1 by this manual operation can be performed by the use of a
movement button provided on the operating panel 20 (see FIG. 1)
arranged on the gantry 1.
[0057] FIG. 8 shows one example of the operating panel 20. A
reference numeral 21 denotes a first movement button for moving the
gantry 1 on the IN side, and a reference numeral 22 denotes a
second movement button for moving the gantry 1 on the OUT side, and
a reference numeral 23 denotes a setting button for setting the
base position of the scan. Moreover, a reference numeral 24 denotes
a display part for producing various displays. Of course, buttons
for other objects can be provided but only the ones necessary for
describing the present invention are shown in the drawing.
[0058] While the operator presses the first movement button 21
(ON), the gantry 1 is moved on the IN side at a predetermined
speed. While the operator presses the second movement button 22
(ON), conversely, the gantry 1 is moved on the OUT side at a
predetermined speed. In both the buttons, when the operator presses
off the button, the button is immediately turned off to stop the
movement of the gantry 1.
[0059] The maximum range of movement of the gantry 1 performed by
this manual operation is stored in the RAM 63a. Then, the gantry 1
can be moved by a remote control from the operating console 200 and
in this case, the gantry 1 is allowed to move only within the
maximum movement range stored in the RAM 63a.
[0060] Here, for example, it is also possible to clear the maximum
movement range stored in the RAM 63a when any one of operations of
moving the gantry 1 to a retracted position (OUT-side movement
limit position), moving the table, and a predetermined operation on
the operating console 200 is performed. However, in order to move
the gantry 1 or to perform a scan by a remote control thereafter,
it is necessary to move the gantry 1 again by the manual operation
to make a check of safety.
[0061] It is possible to ensure safety by limiting the movable
range of the gantry 1 by the remote control in this manner.
[0062] Next, a processing of setting the scan base position in the
embodiment will be described.
[0063] The scan base position can be set by moving the gantry 1 and
pressing the setting button 23 at a desired position. As described
above, however, there is presented the problem that even if the
scan base position is the same for each scan, the setting operation
by the setting button 23 (manual setting operation) needs to be
performed every time, which makes operability worse. In the case
where the manual setting operation is performed every time, a
setting error or a setting miss may be caused.
[0064] Thus, in the embodiment, the scan base position is
automatically set as far as no abnormality is found in the
above-described checking operation performed by moving the gantry 1
by the manual operation after turning on the power.
[0065] A processing of setting the scan base position in the
embodiment will be described in detail by the use of a flow chart
shown in FIG. 9 and FIG. 10.
[0066] FIG. 9 is a flow chart to show a process for setting the
positional relations of the first limit switch S1, the second limit
switch S2, and the desired scan base position, respectively. It is
preferable to perform this process when the system is adjusted.
Further, the above-mentioned desired scan base position is usually
determined in accordance with the installation environment of the
system (such as size of a room).
[0067] First, the operator keeps pressing the second movement
button 22 to move the gantry 1 to the OUT limit position (step S1).
The fact that the gantry is moved to the OUT limit position can be
detected by the fact that the first limit switch S1 is put into
contact with the protrusion 52 to be switched from OFF to ON. At
this time, the gantry is forcibly stopped.
[0068] Next, the operator presses the first movement button 21 to
move the gantry 1 toward the desired scan base position (step S2).
During the movement of the gantry 1, a position z1 where the first
limit switch S1 is switched from ON to OFF (first check point) is
detected and further a position z2 where the second limit switch S2
is put into contact with the protrusion 53 to be switched from OFF
to ON (second check point) is detected, and the distance Ds between
z1 and z2 is stored in the flash memory 63b (step S3)
[0069] Thereafter, when the gantry 1 comes to a desired position as
the scan base position, by the manual operation, that is, by
setting the setting button 23, the desired position z0 is set as
the scan base position (step S4).
[0070] Then, the distance Dr between the position z2 where the
second limit switch S2 is switched from OFF to ON and z0 is stored
in the flash memory 63b (step S5).
[0071] In this manner is finished the process for initially setting
the positional relations of the first limit switch S1, the second
limit switch S2, the desired scan base position, respectively,
which is preferably performed when the system is adjusted.
[0072] FIG. 10 is a flow chart to show a processing of setting the
scan base position which is performed in a checking operation
performed by moving the gantry 1 by the manual operation after
turning on the power or the like. A program corresponding to this
flow chart is stored in the ROM 62 and is executed by the CPU 61
after turning on the power.
[0073] First, at step S11, it is judged based on the input of the
second movement button 22 whether a movement command to the OUT
side is given or not. When the second movement button 22 is pressed
down, the routine advances to step S12 and the gantry 1 starts to
move to the OUT side. Here, in the case where the second movement
button 22 is separated from the operator to be turned off, at this
time, the present process is finished.
[0074] At step S13, it is monitored whether the first limit switch
S1 is turned ON or not during the movement of the gantry 1. Then,
when the first limit switch S1 is turned ON, the routine advances
to step S14 where the movement of the gantry 1 is stopped.
[0075] Next, at step S15, it is judged based on the input of the
first movement button 21 whether a movement command to the IN side
is given or not. When the first movement button 21 is pressed down,
the routine advances to step S16 and the gantry 1 starts to move to
the IN side. Here, also in the case where the first movement button
21 is separated from the operator to be turned off, at this time,
the present process is finished.
[0076] At step S17, it is monitored whether the first limit switch
S1 is switched from ON to OFF or not. Then, when the first limit
switch S1 is turned OFF, at step S18, a position Z1' at this time
is stored in the RAM 63a.
[0077] Next, at step S19, it is monitored whether or not the second
limit switch S2 is switched from OFF to ON during the movement of
the gantry 1. Then, when the second limit switch S2 is turned ON,
at step S20, a position z2' at this time is stored in the RAM
63a.
[0078] Next, at step S21, it is judged whether or not the error
between the distance between the position z1' when the first limit
switch S1 is switched from ON to OFF and the position z2' when the
second limit switch S2 is switched from OFF to ON and the distance
information Ds stored in the flash memory 63b is within a
predetermined range.
[0079] That is, it is judged whether or not the error satisfies the
following equation.
.vertline.(z2'-z1')-Ds .vertline.<T
[0080] where T designates a predetermined threshold value.
[0081] Here, in the case where the above-mentioned equation is not
satisfied, a position detection by any one of the first limit
switch S1, the second limit switch S2, and the pickup sensor 51 is
judged to be not correct and the routine advances to step S22 where
a predetermined error is displayed on the display part 24, or an
alarm sound may be issued to inform the operator of an error. In
any case, in the case of such error, the scan in this state is
prohibited.
[0082] Further, in the case where the above-mentioned equation is
satisfied, the routine advances to step S23 where a position
obtained by adding the distance information Dr stored in the flash
memory 63b to the position z2' when the second limit switch S2 is
switched from OFF to ON is set as the scan base position and where
the obtained base position information is stored in the RAM
63a.
[0083] In the case where the base position in each scan is the
same, as far as no abnormality is found in the checking operation
performed by moving the gantry 1 by the manual operation performed
after turning on the power, the scan base position is automatically
set, so that operability can be drastically improved and the
occurrence of a setting error and a setting miss can be
prevented.
[0084] Further, in the case where an abnormality is caused in a
position detection mechanism provided in the system, the
abnormality is informed and the scan in this state is prohibited,
so that safety can be ensured.
[0085] Here, while the protrusions 52, 53 are provided at the
predetermined positions in the direction of movement of the gantry
1 and the predetermined positions are detected by the use of the
limit switches S1, S2 that are operated when they come in contact
with the protrusions 52, 53 in the embodiment described above, the
predetermined positions can be detected also by the other means,
for example, a combination of an optical sensor and an optical
passing slit, a combination of an optical sensor and an optical
reflector, a magnetic position detection sensor, a position
detection sensor by an electrostatic capacity, a position detection
by an image by means of a CCD camera, and the like.
[0086] Further, while the OUT limit position is made the first
check point and a position where the gantry 1 is moved forward by a
predetermined distance from the first check point is made the
second check point in the embodiment described above, it is also
recommended that a sensor for detecting the first check point and a
sensor for detecting the second check point are provided
independently from each other and that the first check point and
the second check point be provided at the positions that are
detected by both the sensors at the same time when the gantry 1 is
moved to the predetermined position.
[0087] Further, at step S5 in FIG. 9, the distance Dr from the
second check point z2 to the scan base position z0 by the manual
operation is stored, and at step S5 in FIG. 10, the scan base
position is set again by using this Dr, but it is also recommended
that the distance Dr' from the first check point z1 to the scan
base position z0 by the manual operation be stored at step S5 in
FIG. 9 and that the scan base position be set again by using this
Dr' at step S23 in FIG. 10.
[0088] Still further, while two linear guide blocks 42, 43 mounted
on the bottom surface of the gantry base part 2 are mounted on the
linear guide rail 41 in the embodiment described above, as far as
they are fixed with sufficient accuracy so that the direction of
the gantry 1 is not changed, it is also recommended that only one
guide block be used.
[0089] Many widely different embodiments of the invention may be
configured without departing from the spirit and the scope of the
present invention. It should be understood that the present
invention is not limited to the specific embodiments described in
the specification, except as defined in the appended claims.
* * * * *